Acoustic device



Sept. 14, 1943. .1. D. SEABERT ACOUSTIC DEVICE Filed Jan. 51, 1942Patented Sept. 14, 1943 ACOUSTIC DEVICE John D. Seabert, Indianapolis,Ind., assignor to Radio Corporation oi America, a corporation ofDelaware Application January 31, 1942, Serial No. 429,020

6 Claims.

My invention relates to acoustic devices and more particularly toloudspeakers employing large directacting diaphragms. An object of myinvention is to provide a loudspeaker having smaller than usualdimensions, that will faithfully and efiiciently reproduce all usefulsound waves within the frequency range of speech and music.

More particularly, it is an object of my invention -to provide aloudspeaker with a cone diaphragm having a maximum diameter and aflexible base support rim of greatly improved flexibility withoutincreasing the size of the speaker housing or the size of the bailleopening beyond that of the maximum cone diameter.

Heretofore, it has been common practice to suspend a cone diaphragm, atits base, from a speaker housing, or dishpan support, by means of anannular, corrugated centering disc that extends outwardly a substantialdistance from the base of the cone into the rim of the housing, or insome cases to the edge of the opening in a baffle. In these priorconstructions, considerable valuable space has been Wasted as a resultof the space requirements necessary to house the base suspension. Forexample, a cone diaphragm with a 6 inch base required an 8 inch housing.

According to my invention it is possible to provide a practical speakerhaving substantially smaller overall dimensions than heretofore, and atthe same time improved performance. On the other hand, applying theprinciples of my invention, it is possible to provide a speaker withgreatly improved performance for the same overall dimensions asheretofore.

Further, in accordance with my invention, I have provided a loudspeakercharacterized by natural resonance of very low frequency, as of theorder of to &0 cycles, using an inwardly extending base suspension thatis of the usual annular corrugated paper construction and which isadapted to be supported in a simplified and inexpensive manner and tofunction as an effective acoustic seal.

More specifically in accordance With my invention, I have provided ahighly flexible support for the base of a cone diaphragm wherein thecone base suspension extends radially inwardly from the base of the coneand at the same time seals the cone base against leakage of soundpressure around the edge of the cone between the cone and the bafflewithout interfering with the useful radiation of sound Waves.Heretofore, the outwardly extending corrugated annular centering discshave been restricted in size because of the necessity of minimizing thesize of the cone housing. There is considerable space inwardly on thecone base that is available for a centering disc of a size sufficientlygreat in width to proivde the flexibility desired, and I have providedmeans to utilize this space without introducing other disadvantages. Iam aware that attempts have been made heretofore to utilize the spaceinside the cone periphery, possibly for the purpose of increasingflexibility, but such attempts have introduced other disadvantages orcomplications, One of the problems not heretofore solved is that ofproviding an effective acoustic seal around the periphery of the conediaphragm. As an example of prior attempts, reference is made to thefollowing: British Patent 294,285 of 1928, Jensen 2,014,621. It will beobserved that, in these prior attempts,

flexible spiders were attached to the cone diaphragm and supportedcentrally by a rod anchored to the central pole piece. Such anarrangement is necessarily complicated and expensive, interferes witheffectively placing the dustcap at the smaller end of the cone, andcomplicates the acoustic sealing between the base of the cone and asurrounding bafile.

My invention possesses other features and objects, but these will allbecome obvious from the following detailed description of my inventionas illustrated in the accompanying drawing. Referring to the drawing,the single figure is a side elevational view, partly in section, of aloudspeaker embodying my invention.

Referring to the drawing, a frusto-conical dishpan housing I, preferablyof sheet metal, having sound openings 3 surrounds a frusto-conicaldiaphragm 5, preferably of a fairly hard finish paper or other flbrousmaterial suitable for sound radiation, carries an inwardly-extendingsheet metal supp rt member 1. This member is provided with a flange 9for clamping the member to a similar flange II on the cone housing as bymeans of bolts l2. A flexible, corrugated, annular centering disc or webI3 is cemented at its outer periphery to the base peripheral edge of thecone at l5 and extends radially inwardly. It is cemented at its innerperipheral edge to the inner flanged portion 11 of the supporting member1 with an interposed paper gasket It.

This flexible disc 13 is preferably of soft, pliable paper formed withthe corrugations therein by a felting process, 1. e. by the acretion ofpaper and woolen fibers from an aqueous suspension onto a form, andsubsequently pressing, drying, and treating with a waterproofingcompound.

The smaller end of the frusto-conical diaphragm is attached to the usualcylindrical coil form l9 Which carries a voice coil 2| disposed in anannular magnetic air gap at 23. The voice coil is centrally supported inthe air gap with the aid of a concentrically-arranged, corrugatedflexible supporting disc 25 attached to the juncture of the smaller endof the conical diaphragm and the form l9 and supported at its outerperiphery by a cylindrical metal structure 21, flanged at 28. This typeof support is disclosed in Boudette Patent 1,893,049. This disc 25 ispreferably made of cloth impregnated with a resinous compound. A bolt38, extending through holes in pole plate 31, extending through holes inpole plate 31 and dishpan housing I, engages the flange 28 to clamp thedisc 25 in place after the coil 2| has been centered. An

annular piece of felt 28 is disposed around the interior of thecylindrical support 21. A dustcap 29, preferably of paper, is attachedadjacent to the smaller end of the diaphragm for closing the opening inthe smaller end. I have there fore provided an outwardly extendingsupporting disc for the smaller end of the diaphragm, of extensiveradial dimension, and an inwardly supporting disc for the large endthereof, also of large radial extent and unobstructed area,

thereby resulting in a suspension system which is highly flexible in theaxial direction of normal vibratory movement, while exerting the usualrestraint against lateral movement.

The remainder of the speaker assembly is of conventional design andconsists of a U-shaped yoke 3| of mild steel, and an inner pole 33 ofsimilar material around which there is disposed a field coil 35.Fastened to the ends of the U- shaped yoke by means of screws 30 is thetop pole plate 37 having a circular opening at 23 which forms with thecenter pole piece 24 an annular air gap, mentioned above, into which thevoice coil extends. The top pole plate 37 is also bolted to the smallerend of the dishpan or cone housing. Instead of a field coil, a permanentmagnet may of course be used.

The finished speaker is adapted to be positioned against a bailie ofconventional form as illustrated at 39, the outer cylindrical portion ofthe support element 1 preferably fitting into the baffle opening 4|. Thebafile may be of the usual flat type, directional type or the cabinettype.

It will be apparent that, in accordance with my invention, the inwardlyextending base suspension arrangement results in greater flexibility andgreater fidelity of reproduction of lower audio frequency waves, givesthe usual acoustic seal,

and results in a smaller outside diameter of loudspeaker housing for agiven si Ze cone diaphragm. Although the present support structure forthe base of the cone would appear to obstruct a substantial. effectivelyradiating area of the cone, it has been found that there issubstantially no obstruction in the acoustic sense. For low frequencywaves such an obstruction has no effect, so long as the corrugatedsuspension I3 is soft and pliable and thereby avoids introducing anout-of-phase cancellation effect with respect to the sound pressure fromthe adjacent diaphragm portion. For high frequencies, the centralportion of the cone is most effective and such portion is not obstructedby the supporting structure.

In assembling my loudspeaker the following procedure is used: Theannular supporting element 1 is placed horizontally with the inner andouter peripheral edges or flanges facing upwardly. Cement is appliedaround the top surface of flange I? which is then horizontal. A papergasket is applied to this portion as shown at l8. More cement is appliedto this gasket. The corrugated centering disc l3, to which the base ofthe cone has been attached at 15, is dropped into the position shownwith the inner circular edge of the disc fitting closely around the thenupstanding flanged edge 20 of the metal member 7 in guiding relation.The lower surface of the inner edge portion of the disc I3 is caused tobe pressed against the member l8, until the cement hardens, by reason ofthe vertical weight of the cone diaphragm which carries the voice coiland centering disc 25 and its support structure 27.

A sub-assembly is thereby formed consisting of diaphragm 5, centeringdisc I3, support element 1, voice coil 23 and its centering structure 25and 21. The sub-assembly, as a unit, is thereafter assembled into theposition shown on the cone housing and clamped in place by means ofbolts l2 and 38 after centering of'the voice coil in the airgap. Thedustcap 29 is finally cemented in place.

My present invention may be applied to a standard dishpan, or housing,by providing a flanged supporting element like I, which can be bolted tothe flange of the standard housing dishpan heretofore used for securingthe outer edge of the annular flexible supporting disc of the diaphragmand, of course, making the cone of larger diameter. In other words,referring to'the drawing, the supporting element 1 may be considered asan adapter to be used on a standard cone housing to make it possible tosubstitute a larger cone diaphragm for the one ordinarily used. It will,therefore, be appreciated that my invention is of a highly simplifiedand practical nature. While I have shown a conical diaphragm of circularcontour, it may be made in other suitable shapes, such as elliptical incontour. Furthermore, the diaphragm may be of the so called morningglory shape. Instead of frustoconical, it may terminate in a point, i.e., it may be conical. The particular shape of the diaphragm is no partof my present invention, and it is intended that the terms conical, ordished, shall define any of these Well known types. Since this inventionis capable of considerable variation and modification and should not beconstrued as limited to the particular structure described andillustrated, but only in accordance with the appended claims.

I claim as my invention:

1. In an acoustic device, a direct acting conical diaphragm, meansremote from the base of said diaphragm for vibrating said diaphragm inaccordance with audio frequency energy; means for flexibly supportingthe base periphery of said diaphragm for axial vibratory movement andagainst lateral movement comprising an annular stationary memberextending inwardly from the region of said base periphery, and aflexible annular disc member attached to said base periphery andextending inwardly into acoustic sealing engagement with said stationarymember.

2. In an acoustic device, a direct acting dished diaphragm having aperipheral edge and a central portion, an actuating device connected tothe said diaphragm central portion, a flexible annular disc memberhaving its outer periphery attached around the peripheral edgeof saiddiaphragm as an acoustic seal and extending a substantial distanceradially inwardly therefrom, a

housing disposed externally of said diaphragm, and a supporting membercarried by said housing and extending inwardly beyond said peripheraledge and secured to said disc member at its inner periphery andsubstantially free of contact with the remaining portions thereof.

3. In an acoustic device, a frusto-conical diaphragm, a frusto-conicalhousing for said diaphragm, the base of said housing being disposedadjacent the base of said diaphragm, an annular rigid supporting memberattached to said housing base and extending radially inward beyond saiddiaphragm base, and an annular flexible disc member attached at itsouter periphery to said diaphragm base and attached at its innerperiphery to said support member, thereby providing a base suspension ofsubstantial unobstructed radial area.

4. In an acoustic device, a frusto-conical diaphragm of stiff fibrousmaterial, a frusto-conical sheet-metal housing disposed externally ofsaid diaphragm with its base terminating adjacent the base of saiddiaphragm, an annular sheet metal supporting member carried by saidhousing and extending radially inwardly beyond the base periphery ofsaid diaphragm whereby to form an opening concentric with and smallerthan the base periphery of said diaphragm, and a pliable web memberattached to said supporting member around said opening and extendingradially outwardly into operative engagement with the base of saiddiaphragm.

5. In combination, an acoustic bafiie having a sound opening, astationary supporting member disposed inoperative engagement with saidbaflle around said opening and extending inwardly toward the center ofsaid opening, a dished acoustic diaphragm having a base diameterexceeding the inner dimension of said supporting member, a housingdisposed around said diaphragm, said housing being attached to saidsupporting member, and an annular flexible Web member attached at itsouter periphery to the base of said diaphragm and extending radiallyinwardly into fixed engagement with said supporting member only at anannular portion thereof substantially spaced radially from saiddiaphragm base.

6. In combination, an acoustic bafiie having a sound opening therein,housing structure for supporting a dished diaphragm substantially inconcentric relation with respect to said opening, an annular supportingmember carried by said housing structure and disposed around saidopening and extending inwardly therefrom, a dished diaphragm within saidhousing, said diaphragm having a base dimension exceeding the innerdimension of said supporting member, and an annular flexible web memberattached around the base of said diaphragm and extending inwardly intoengagement with the inner periphery of said supporting member and freeof contact with the remaining portions of said supporting member,whereby said web member and said supporting member constitute anacoustic seal between said diaphragm and said baffle.

JOHN D. SEABERT.

